In conveyor systems for conveying and distributing articles, a series of conveyed articles are typically transported along moving conveying surfaces. Such conveyor systems will typically include one or more sortation devices which divert selected articles from a primary conveying path onto one or more secondary conveying paths.
Sortation devices often employ pusher elements which are mounted relative to the conveying surface. Often, the pusher elements are mounted such that they may be selectively moved across the conveying surface in order to eject an article from the primary conveying path onto a secondary conveying path or other location. One particular sortation device of this type is referred to as a “shoe sorter,” wherein the pusher elements are termed “shoes.”
In a typical shoe sorter, the primary conveying surface is provided by a plurality of transverse tubes (rollers) or slats that form the transport surface. A plurality of pusher elements that are part of, or supported by, the transport surface and are guided in a set position along the length of the sorter during normal forward operation. The pusher elements can take on many forms such as belted slats, pins, and molded blocks. Historically the most prevalent design is referred to as a shoe, although other designs are possible. Here after the term shoe and pusher element shall be used to include all conventional shoes, as well as other diverting elements such as but not limited to slats, belts, rollers, etc. When it is necessary to direct an article from the main conveyor run to an adjacent takeaway conveyor, a switch mechanism causes an assigned set of pusher element to be diverted to slide across the conveyor surface in a diagonal direction. The diverted shoes thus engage and divert the article to a secondary conveying path, such as a takeaway conveyor. Such shoe sorters often use guide tracks or guide surfaces which direct the assigned set of shoes laterally across the conveying surface, while shoes which are not assigned continue to travel along the conveying surface in their set position.
In these shoe sorters and other types of sortation devices, the control system ensures that the appropriate set of pusher elements is assigned to each carton, and that the assigned pusher elements are directed across the primary conveying surface at the proper time. Sorter throughput depends on a variety of factors, particularly the speed of the conveying surface and the size of the gap between adjacent articles being sorted. If the size of the gap is small, it can be difficult for the control system to not only assign the proper set of pusher elements, but also ensure that the assigned set of pusher elements are diverted across the conveying surface at the proper time.